1. Field of the Invention
The present invention relates to an optical recording medium, particularly to an optical waveguide recording medium, which has an optical waveguide provided with refractive index-discontinuous portion to guide a light beam thereon the produce reflection of the guided beam having different amplitudes and phase delays, and which is capable of permitting recorded information to be reproduced as a time-series signal waveform from part of the reflected light and to a playing apparatus therefore.
2. Description of the Related Art
Japanese Unexamined Patent Publication No. 2-210627 discloses such an optical waveguide recording medium and a playing apparatus therefore. Further, a playing apparatus for an optical waveguide recording medium has been proposed which has a Mechelson interferometer type optical heterodyne detecting optical system. This reproducing apparatus comprises a collimator lens for converting a radiated light beam from a light source into a flux of parallel light, a half mirror for causing divergence of a light beam to be guided on an optical waveguide recording medium, an objective lens for coupling one part of the divided light beam to the optical waveguide of the recording medium, a movable mirror for imparting a phase shift and a frequency shift to the other part of the divided light beam to provide reference light, and a photodetector for causing interference between the signal light reflected by and returning from refractive index-discontinuous portions formed on the optical waveguide and the reference light for heterodyne detection of the optical output.
Since this reproducing apparatus utilizes the movable mirror as a means to subject the divided light beam to phase shift and frequency modulation for heterodyne detection, the modulation frequency is limited, thus restricting the improvement of the information recording density. What is more, the presence of the mirror driving section stands in the way of achieving miniaturization of the reproducing optical system and improvement of its reliability.